How can I create a countdown timer in Cycles?
Please have a try with this script By Respected fellow: batFINGER:

import bpy
import math
from bpy.props import BoolProperty
def countdown_timer(scene):
    # look for all font objects with _timer property
    timers = [ob.data for ob in scene.objects if ob.type == 'FONT' and ob.data.is_timer]
    for font in timers:
        secs = font["timer"]
        countdown_frames = secs * scene.render.fps / scene.render.fps_base
        frame = countdown_frames - scene.frame_current + 1 
        if frame &lt; 0:
            continue
        t = float(frame * scene.render.fps_base ) / float(scene.render.fps)
        minutes = t // 60
        t %= 60
        seconds = math.floor(t)
        t = t - seconds
        hundreds = math.floor(100 * (t))
        font.body = "%02d:%02d:%02d" % (minutes,seconds,hundreds)
    return None
def is_timer(self, context):
    if self.is_timer:
        if "timer" not in self.keys():
            self["timer"] = 10 # 10 seconds default
    return None
class TimerPanel(bpy.types.Panel):
    """Timer Panel"""
    bl_label = "Countdown Timer"
    bl_idname = "FONT_PT_timer"
    bl_space_type = 'PROPERTIES'
    bl_region_type = 'WINDOW'
    bl_context = "data"

    @classmethod
    def poll(cls, context):
        return (context.object and context.object.type in {'FONT'} and context.curve)
    def draw_header(self, context):
        font = context.object.data

        self.layout.prop(font, "is_timer", text="")
    def draw(self, context):
        font = context.object.data
        layout = self.layout
        if font.is_timer:
            row = layout.row()
            row.prop(font,'["timer"]', text="Seconds")
def register():
    bpy.types.TextCurve.is_timer = BoolProperty(default=False, update=is_timer, description="Make countdown timer")

    bpy.app.handlers.frame_change_pre.append(countdown_timer)    
    bpy.utils.register_class(TimerPanel)

def unregister():
    bpy.utils.unregister_class(TimerPanel)
    bpy.app.handlers.frame_change_pre.pop()

if __name__ == "__main__":
    register()


Copy it to the Text Editor 


Dont forget to hit run script 

Create a new text  and you will get a new option box under fonts.


Adjust the value as per your needs



Play it! It can be used in Cycles or gaming engine !

You will have a full control of materials fonts size and rotations etc

Best of luck